1. Technical Field
The present disclosure relates to electrosurgical devices suitable for tissue ablation applications and, more particularly, to methods and systems for enhancing ultrasonic visibility of energy-delivery devices within tissue.
2. Discussion of Related Art
Treatment of certain diseases requires the destruction of malignant tissue growths, e.g., tumors. Electromagnetic radiation can be used to heat and destroy tumor cells. Treatment may involve inserting ablation probes into tissues where cancerous tumors have been identified. Once the probes are positioned, electromagnetic energy is passed through the probes into surrounding tissue.
In the treatment of diseases such as cancer, certain types of tumor cells have been found to denature at elevated temperatures that are slightly lower than temperatures normally injurious to healthy cells. Known treatment methods, such as hyperthermia therapy, heat diseased cells to temperatures above 41° C. while maintaining adjacent healthy cells below the temperature at which irreversible cell destruction occurs. These methods involve applying electromagnetic radiation to heat, ablate and/or coagulate tissue. Microwave energy is sometimes utilized to perform these methods. Other procedures utilizing electromagnetic radiation to heat tissue also include coagulation, cutting and/or ablation of tissue.
Electrosurgical devices utilizing electromagnetic radiation have been developed for a variety of uses and applications. A number of devices are available that can be used to provide high bursts of energy for short periods of time to achieve cutting and coagulative effects on various tissues. There are a number of different types of apparatus that can be used to perform ablation procedures. Typically, microwave apparatus for use in ablation procedures include a microwave generator that functions as an energy source, and a microwave surgical instrument (e.g., microwave ablation probe) having an antenna assembly for directing energy to the target tissue. The microwave generator and surgical instrument are typically operatively coupled by a cable assembly having a plurality of conductors for transmitting microwave energy from the generator to the instrument, and for communicating control, feedback and identification signals between the instrument and the generator.
There are several types of microwave probes in use, e.g., monopole, dipole and helical, which may be used in tissue ablation applications. In monopole and dipole antenna assemblies, microwave energy generally radiates perpendicularly away from the axis of the conductor. Monopole antenna assemblies typically include a single, elongated conductor. A typical dipole antenna assembly includes two elongated conductors that are linearly-aligned and positioned end-to-end relative to one another with an electrical insulator placed therebetween. Helical antenna assemblies include helically-shaped conductor configurations of various dimensions, e.g., diameter and length. The main modes of operation of a helical antenna assembly are normal mode (broadside), in which the field radiated by the helix is maximum in a perpendicular plane to the helix axis, and axial mode (end fire), in which maximum radiation is along the helix axis.
During certain procedures, a probe may be inserted directly into tissue, inserted through a lumen, e.g., a vein, needle or catheter, or placed into the body using surgical techniques. Multiple probes may be used to synergistically create a large ablation or to ablate separate sites simultaneously.
Ultrasonography or computed tomography (CT) guidance may used prior to ablation treatments for aiding probe placement. Ultrasonography is the imaging of deep structures in the body by recording the echoes of pulses of high frequency ultrasonic or sound waves directed into tissue and reflected by tissue planes where there is a change in density. A change in density exists along the plane or boundary between two types of tissue or between tissue and a non-anatomical structure, such as an energy-delivery device, such as, for example, an ablation probe within the tissue. Due to different acoustic impedances among the different types of anatomical structures, and non-anatomical structures within tissue, ultrasonography produces visual images of the anatomical and non-anatomical structures within the body.
However, during certain surgical procedures, it can be difficult to visualize an ablation probe, needle, catheter, etc. within the body using ultrasonography. As a result, it is difficult to guide surgical instruments to a proper location and/or position within the body, such as, for example, an ablation probe within a tissue mass to be ablated. Hence, techniques and improvements are needed to enhance the visualization of surgical instruments, especially, energy delivery devices, within tissue during ultrasonography.